Thread: Question about using the toString method.

Hi everyone. I'm writing a program that is using a class called Coin.java, that flips a coin. The program is supposed to find the longest run of Heads in 100 flips of the coin. I'm having trouble returning the final value of how many heads were flipped. In order to return this value I need to use the toString method that is included in the Coin class that was provided from my lab book. What paramaters am I supposed to put in the "System.out.println()" statement in order to return the toString? Below is the Coin class with my program below it. Thanks for your help!

Coin class

public class Coin
{
	public final int HEADS = 0;
	public final int TAILS = 1;
	private int face;
// ---------------------------------------------
// Sets up the coin by flipping it initially.
// ---------------------------------------------
	public Coin ()
	{
		flip();
	}
// -----------------------------------------------
// Flips the coin by randomly choosing a face.
// -----------------------------------------------
	public void flip()
	{
		face = (int) (Math.random() * 2);
	}
// ---------------------------------------------------------
// Returns true if the current face of the coin is heads.
// ---------------------------------------------------------
	public boolean isHeads()
	{
		return (face == HEADS);
	}
// ----------------------------------------------------
// Returns the current face of the coin as a string.
// ----------------------------------------------------
	public String toString()
	{
		String faceName;
		if (face == HEADS)
			faceName = "Heads";
		else
			faceName = "Tails";
		return faceName;
	}
}

Runs program

public class Runs
{
	public static void main (String[] args)
	{
		final int FLIPS = 100; // number of coin flips
		int currentRun = 0; // length of the current run of HEADS
		int maxRun = 0; // length of the maximum run so far
		int countH;
 
		Coin coin1= new Coin(); // Create a coin object
 
		coin1.flip(); // Flip the coin FLIPS times, Since flip methods returns "void", no parameters.
 
		for (int i = 0; i < FLIPS; i++)
		{
			currentRun=i;
			coin1.flip();// Flip the coin & print the result
			System.out.println(coin1);
			System.out.println("Current run is: " + currentRun);// Update the run information
		}
 
		// Print the results
		System.out.println(         );
	}
}

The toString() method returns a String, and System.out.println() can take a String as a parameter. In other words, just pass the String you want to display into the System.out.println() method.

So based on the first code above(the Coin class), would I do something like "System.out.println(faceName);" ? Or how would I get the program to return the value in the toString method in the Coin class?

Thanks for chiming in Norm. When I try "System.out.println(faceName);" the compiler still says that "faceName cannot be resolved to a variable".

Originally Posted by Norm

Where is the variable faceName defined? You can not use a variable whose definition is not in scope at that location.

public String toString()
	{
		String faceName;
		if (face == HEADS)
			faceName = "Heads";
		else
			faceName = "Tails";
		return faceName;
	}
}

In this piece of code from the Coin class isn't it defined as "String faceName"? Or is it the private int face?

Nope. No errors in the class itself or the toString method. I only get an error when I try to use System.out.println(faceName); or System.out.println(face); or however else I try to call the toString.

Originally Posted by Norm

Do you understand what the scope of definition for a variable is? You can not use a variable if it is not defined or if the definition for the variable is out of scope (not inside of the enclosing pair of {}s)

Where is the definition of faceName in relation to where your trying to reference it? It must not be in scope because the compiler is giving an error. If the only definition for faceName is inside of the toString() method, then that is the only place that you can reference faceName.

Than how can I reference the toString?

toString method is to format whatever you want to print out from a class (object).

The general form is Object newObject = new Object(Constructor parameters );
The toString method doesn't need anything to passed in. You call it by calling the Object itself using System.out.print(newObject);